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reducing the rollback segment from oracle

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Danny Pogi
Advisor

reducing the rollback segment from oracle

hi guys,

does the rollback segment in oracle clears itself after commiting a transaction?

because i have seen from one of our boxes that the tablespace allocated to RBS is quite big and i want to deallocate some of this to other tablespace. is it safe to remove reduce rbs?

(hp-ux version is 10.20 oracle 8.0.4)

thanks,

danny
7 REPLIES
Ian Lochray
Respected Contributor

Re: reducing the rollback segment from oracle

Oracle will not immediately shrink a rollback segment when a transaction is committed. The time taken to automatically shrink depends on the setting of the OPTIMAL storage clause and whether other transactions are reading the data held in the rollback segment.
You can manually shrink a rollback segment by issuing a command like -
ALTER ROLLBACK SEGMENT rbs1 SHRINK TO 100K;
T G Manikandan
Honored Contributor

Re: reducing the rollback segment from oracle

alter rollback segment xyz shrink to xxx M;

Christian Gebhardt
Honored Contributor
Solution

Re: reducing the rollback segment from oracle

Hi
extract from Oracle-PDF-Doku

Chris
Ravi_8
Honored Contributor

Re: reducing the rollback segment from oracle

Hi, Danny

svrmgrl> alter rollback segment shrink to

K -- size in KB
M -- size in MB
never give up
Jean-Luc Oudart
Honored Contributor

Re: reducing the rollback segment from oracle

fiel attached document from Metalink.
I assume you're an Oracle customer and therefore have access (once registered) to this web site.
You may find other information regarding your question

Jean-Luc
fiat lux
Andreas D. Skjervold
Honored Contributor

Re: reducing the rollback segment from oracle

Hi

Be careful not to reduce the RBS tablespace too much after reducing the rollback segments as this might result in errors when the rollback segment expands due to large transactions.

also you should not set the OPTIMAL size too low as Oracle then will spend more time allocation and deallocationg space for the rollback segments.

Andreas
Only by ignoring what everyone think is important, can you be aware of what everyone ignores!
Alexander M. Ermes
Honored Contributor

Re: reducing the rollback segment from oracle

Hi there.
Set the OPTIMAL parameter for the rollback segements. That will help, but it might take a while. You can also use the Oracle Enterprise Manager to shrink the rollback segments
( Tools -> Database applications -> Storage Manager -> ORACLE_SID -> rollback segments ).

Reducing the RBS tablespace might be the reason for future problems.
If you run large amounts of data manipulating
Oracle statements, you will need the actual space. We have this problems, because we do a database refresh from an external database every day. Our database is not too big, but the amount of data coming over requires some big RBS tablespace. If you go for automatic committing, do not forget, that you might have trouble, if your job breaks off half way through.
Just my 2 ct.
Rgds
Alexander M. Ermes
.. and all these memories are going to vanish like tears in the rain! final words from Rutger Hauer in "Blade Runner"